You set up your VoIP and have started making inbound and outbound calls. Everything is all great, but then for no apparent reason, you notice that not all calls are of good quality, maybe you hear your friends, but they can not hear you, or perhaps your phone won’t stop ringing even though you picked it up.
These are not the problems you would expect from a VoIP service. Don’t worry, and let us introduce you to SIP ALG – the cause of these above problems.
What is SIP ALG? This article will explain to you the meaning, functions, and applications of SIP ALG. And why does SIP ALG affect VoIP calls? Do not hesitate to read our post now!
What is SIP ALG? Function And Typical SIP ALG Technology Application
What is SIP ALG?
SIP stands for the phrase Session Initiation Protocol, the basic service that powers all VoIP (Voice over Internet Protocol) devices, apps, and phones. SIP maintains call presence, monitors the call audio, and manages registered devices.
This service is more and more popular with packets involved in embedded IP addresses, and concerns in a SIP exchange are relatively complex. Besides, firewall system NAT (Network Address Translation) is also a challenge for SIP because it divides the network into public and private domains.
ALG was created to make it easier for SIP to bypass the firewall system NAT by accessing the payload of outgoing packets (and incoming packets) and translating embedded private addresses into the correct public addresses.
So what is ALG? ALG (Application Layer Gateway) is a gateway, otherwise known as a firewall, that rewrites specific application layer data fields.
SIP ALG is a combination of two technologies: SIP and ALG. SIP ALG acts as a firewall found in most networked routers to minimize NAT.
See also: What Is SIP Trunking?
Function of SIP ALG
- Synchronize multiple chains or instances between servers.
- ALG does a similar thing to NAT translation.
- Before the app messages leave the router, SIP ALG intercepts them. Then inspects and replaces the private client IP in Port with the router’s public IP.
- SIP ALG allows users to see peer status because ALG supports SIP by using the SIP Publish method.
- For auditing purposes, SIP ALG creates log messages.
- Routes traffic for VoIP applications and ensures the use of standard SIP protocols in VoIP links.
- Opens the ports necessary to exchange video media and audio and to receive and make calls.
- Identifies application-specific commands and provides security controls for those applications.
- SIP ALG allows clients applications to use UDP/TCP to connect with the server application. Without ALG, ports are closed, or a large of the ports in the firewall need to be opened by the network administrator, weakening the network and enabling future attacks on those ports.
Typical SIP ALG Technology Application
SIP ALG is often used in VoIP service for apartment buildings. We have an illustrative example through the image below.
Each user in an apartment building will have an IP address from the individual address range. The mission of SIP ALG is to convert these personal IP addresses correctly into public IP addresses.
Besides, SIP ALG must also ensure that VoIP calls from the public addresses are successfully transferred to the correct users on the private addresses.
SIP ALG Signs Impact VoIP Calls
Even though SIP ALG was created to improve the connections and minimize the NAT system, in many cases, it modifies unwanted SIP packets, resulting in malfunctions, disconnected VoIP, even calling failed. Let us explore some of the effects of SIP ALG on VoIP calls:
- For some unknown reason, incoming calls automatically go straight to voice messages.
- Phones can not receive calls, or VoIP has one-way audio, meaning only one person can hear the other.
- The call is automatically turned off after connecting.
- When a call comes in, the phone does not ring.
- The phone won’t stop ringing even though you picked it up.
The recipient will receive an invitation via the internet when you make an outbound call. An invite response is then sent back to confirm that the connection has been made.
The time the call is answered, a final acknowledgment is sent to verify the linkage, and a conversation can then occur. Typically, all of these steps take place in seconds during SIP calls.
When SIP ALG is active, it can modify these message’s SIP packets in the unexpected direction: corrupt them or make them unreadable. These can lead to different results from the call being dropped, rejected to loss of audio, or fail registrations.
To solve these situations, we advise you to turn SIP ALG off from the firewall and router. Once it gets disabled, you will have to find that all your problems disappear.
Read more: What Is Sip Calling?
How do you turn off SIP ALG?
There are many different rooters, and each one has its interface, but generally, there will be a check box or button that will allow you to disable it. What you need is to access the Reuters interface. You can usually find these details from the bottom or side of the router itself.
The information you need is the IP address and the login credentials. Enter the address bar’s IP after opening a browser window, followed by the login details when requested on the VT Business hub five Rita.
A great way to find the SIP ALG is to go to advanced settings, enter the password again it requested. Then, click the firewall followed by configuration and scroll down to the application layer; click yes next to the disables SIP ALG.
Finally, click to apply and save any changes made, and then reboot the router. It is also good to reboot any phones connected to the router to ensure that the new settings take effect.
Conclusion
Our article “What is SIP ALG” will help you better understand SIP ALG, its functions, and applications to improve the connections. However, SIP ALG also harms your VoIP calls, such as incoming calls automatically go straight to voice messages, phones can not receive calls, or VoIP has one-way audio.
After learning the features and effects of SIP ALG on your VoIP calls, you can consider whether to disable it. If you want to turn it off to improve VoIP calls, you can follow the instructions above.
We hope that you have great VoIP calls without interruption!
